1. Field of the Invention
The present invention relates to an endoscope system for producing a biological function information image, which images biological function information including the amount of hemoglobin in blood, an oxygen saturation level, and the like, and an operating method thereof.
2. Description Related to the Prior Art
In recent medical care, an endoscope system that is provided with a light source device, an endoscope device, and a processor device is widely used. In an endoscopic diagnosis using this endoscope system, not only normal light observation that uses white light being broad band light as illumination light, but also special light observation that emphasizes a blood vessel of an observation object in display by using narrow band light in a narrowed wavelength band has become widespread.
Besides the special light observation, it is performed to calculate biological function information, including the amount of hemoglobin, an oxygen saturation level, and the depth of a blood vessel, from an image signal obtained by the endoscope system with the use of a light absorption property of the blood vessel and a scattering property of living body tissue, and image the calculated biological function information. For example, a pseudo color oxygen saturation image, which is colored in accordance with the magnitude of the oxygen saturation level, is produced in Japanese Patent No. 2648494. This oxygen saturation image facilitates finding out a cancer being in a hypoxic state.
Since the biological function information is obtained by an arithmetic process based on the image signal, the correctness of the oxygen saturation level itself is reduced unless the image signal is obtained in an appropriate imaging condition. For example, when a pixel value of the image signal is abnormally high because of too high intensity of the illumination light applied to the observation object, the correctness of the oxygen saturation level obtained from that image signal is regarded to be low.
Against this problem, according to Japanese Patent No. 2768936 and U.S. Pat. No. 5,956,416 corresponding to Japanese Patent No. 3217343, an area in which the pixel value of the image signal is beyond a certain threshold value is detected as an abnormal area, and processing and control for differing display of this abnormal area from that of a normal area in which the pixel value is not beyond the threshold value (for example, by masking) are performed. This allows a user to easily distinguish an incorrect area from an area having the correct biological function information such as the oxygen saturation level.
According to the method of distinguishing the abnormal area from the normal area using the certain threshold value as a border, as described in the Japanese Patent No. 2768936 and the U.S. Pat. No. 5,956,416, if the pixel value of the abnormal area largely exceeds the threshold value, in other words, in the case of the occurrence of halation, the reliability of the oxygen saturation level is precisely reflected in display of the abnormal area on a screen. However, although an area is judged to be the abnormal area, if the pixel value of the abnormal area is just slightly above the threshold value and the actual reliability of the oxygen saturation level is not low, the reliability of the oxygen saturation level is not precisely reflected in display of the abnormal area on the screen. On the contrary, although an area is judged to be the normal area, if the pixel value of the normal area is just slightly below the threshold value and the actual reliability of the oxygen saturation level is low, the reliability of the oxygen saturation level is not precisely reflected in display of the normal area on the screen. Therefore, there is a demand for an endoscope system that can precisely display the reliability of the biological function information such as the oxygen saturation level.